1. Field of the Invention
The present invention relates to a method for manufacturing a capacitor for semiconductor devices, and more particularly, to a method for manufacturing a capacitor for semiconductor devices having a TaON film as its dielectric layer.
2. Description of the Related Art
Recently as the level of integration in semiconductor devices has increased, much research and developments have been directed toward reducing the effective cell area and reducing the devise operation voltage. In these efforts, as the unit area available for the capacitor formation has reduced remarkably, the electric charge needed to operate memory devicesxe2x80x94that is the capacitance per unit areaxe2x80x94needs to be increased.
Accordingly, conventional methods to obtain sufficient capacitance values have included: increasing the area for capacitor formation by modifying the structure of the widely used cylinder structure; reducing the thickness of a dielectric film; and substituting the silicon oxide which forms the dielectric film with a NO (Nitride-Oxide) or ONO (Oxide-Nitride-Oxide) structure, or Ta2O5 or BST (BaSrTiO3) which can provide higher capacitance values due to their high dielectric constant (20 to 25).
Recently, because of the limitations inherent in capacitors having a NO dielectric in providing sufficient capacitance that is needed for the next generation of memory devices, such as DRAM""s with 256M or greater, the use of a Ta2O5 dielectric film has been receiving subject of the active research and development efforts. However, the Ta2O5 thin film has an unstable stoichiometry that generates displaceable Ta atoms with oxygen vacancies due to an unbalanced composition ratio between the Ta and O atoms present in the thin film. In addition, during the formation of a dielectric film, such impurities as carbon atoms (C) and carbon compounds (CH4 or C2H4) and water H2O are generated from the reaction between the organic portion of Ta(OC2H5)5xe2x80x94a precursor of Ta2O5xe2x80x94and O2 gas. Consequently, due to the carbon atoms as well as other ions and free radicals existing in the Ta2O5 thin film as impurities, the resulting capacitors tend to exhibit increased leakage current and degraded dielectric characteristics.
To remove or significantly reduce such impurities in the Ta2O5 thin film, a low temperature heating treatmentxe2x80x94for example plasma N2O or UV-O3xe2x80x94is performed twice or three times. However, this heat treatment makes a manufacturing process complicated, and since the Ta2O5 thin film is susceptible to oxidation, the lower electrode may be oxidized during the heat treatment.
To improve the unstable stoichiometry of the Ta2O5, the dielectric film of a capacitor is replaced by TaON. Since TaON has a dielectric constant over 25, it has high permitivity and the chemical composition structure is more stable than the Ta2O5 thin film, thus generating less oxidation reaction with the lower electrode.
Further, a capacitor using TaON can reduce the thickness of an equivalent oxide film (Tox) than capacitors having the NO or Ta2O5 dielectric. Additionally, the TaON capacitor is strong to an electric impact applied from the outside and has a high breakdown voltage while having a low leakage current.
However, because Ta(OC2H5) is sued as a Ta source gas and O2 or NH3 which is used as a reaction gas during deposition of TaON, carbon and hydrogen impurities are still present in the Ta2O5 thin film so the resultant capacitors tend to exhibit degraded dielectric characteristics.
To solve the above problems, it is an objective of the present invention to provide a method for manufacturing a capacitor for a semiconductor device by which a capacitor suitable for a highly integrated semiconductor device can be obtained by using a dielectric film having a high dielectric constant and superior electric characteristics.
Also, it is another objective of the present invention to provide a method for manufacturing a capacitor for a semiconductor device which can reduce leakage current and improve electric properties of the semiconductor device.
Accordingly, to achieve the above objectives, there is provided a method for manufacturing a capacitor for a semiconductor device comprising the steps of forming a lower structure on a semiconductor device, forming a lower electrode on the lower structure of the semiconductor device, forming a dielectric thin film by depositing an amorphous TaON film on the surface of the lower electrode, and supplying the source gas of a Ta component in a mono-pulse manner and continuously supplying a reaction gas even when the Ta source gas is not supplied, and forming an upper electrode on the upper portion of the dielectric thin film.
According to another embodiment of the present invention, there is provided a method for manufacturing a capacitor for a semiconductor device comprising the steps of forming a lower structure on a semiconductor device, forming a lower electrode on the lower structure of the semiconductor device, nitrifying the surface of the lower electrode by plasma or through a metal thermal process, forming an amorphous TaON film on the surface of the lower electrode, and supplying a Ta source gas in a mono-pulse manner and continuously supplying a reaction gas even when the Ta component gas is not supplied, crystallizing the amorphous TaON film by a metal thermal process or an annealing process, forming an upper electrode on the upper portion of the dielectric film.